[Paper Review] Impact of electrostatic crosstalk on spin qubits in dense CMOS quantum dot arrays

Jesús D. Cifuentes, Tuomo Tanttu+21 more|arXiv (Cornell University)|Sep 4, 2023

Advancements in Semiconductor Devices and Circuit Design4 citations

TL;DR

This paper establishes a theoretical framework explaining how electrostatic crosstalk from neighboring gates in CMOS quantum dot arrays induces Stark shifts in silicon spin qubits via spin-orbit coupling. It demonstrates that gate-induced electric fields tune qubit Larmor frequencies with measurable variability, and identifies the [100] crystal direction as optimal for minimizing dephasing and g-factor fluctuations, enabling scalable global control in large-scale quantum processors.

ABSTRACT

Quantum processors based on integrated nanoscale silicon spin qubits are a promising platform for highly scalable quantum computation. Current CMOS spin qubit processors consist of dense gate arrays to define the quantum dots, making them susceptible to crosstalk from capacitive coupling between a dot and its neighbouring gates. Small but sizeable spin-orbit interactions can transfer this electrostatic crosstalk to the spin g-factors, creating a dependence of the Larmor frequency on the electric field created by gate electrodes positioned even tens of nanometers apart. By studying the Stark shift from tens of spin qubits measured in nine different CMOS devices, we developed a theoretical frawework that explains how electric fields couple to the spin of the electrons in increasingly complex arrays, including those electric fluctuations that limit qubit dephasing times $T_2^*$. The results will aid in the design of robust strategies to scale CMOS quantum technology.

Motivation & Objective

• To understand how electrostatic crosstalk from adjacent gates affects spin qubit properties in dense CMOS quantum dot arrays.
• To quantify the impact of electric fields on qubit Larmor frequency via spin-orbit interactions and interface disorder.
• To identify optimal magnetic field orientations that minimize dephasing and g-factor variability in spin qubits.
• To develop a scalable framework for characterizing gate-specific Stark shift tunability across multiple qubits.
• To enable robust global control protocols in large-scale silicon spin qubit processors by accounting for electric field coupling effects.

Proposed method

• Measured Stark shifts across 30 spin qubits in nine different CMOS devices using qubit spectroscopy.
• Developed a theoretical model linking electric field gradients to g-factor shifts via spin-orbit coupling: $ \frac{dg_n}{dV_g} = \frac{dx}{dV} \cdot \vec{\nabla}g $.
• Performed atomistic simulations of MOS quantum dots on rough SiO₂ interfaces to model disorder effects.
• Mapped the dependence of $ T_2^* $ on magnetic field orientation to isolate electric noise contributions.
• Correlated individual qubit Stark shift tunability with $ T_2^* $ profiles to validate the model.
• Used a linear combination of virtual gates to simulate individual qubit control, informed by measured $ \frac{dg_n}{dV_g} $ parameters.

Experimental results

Research questions

• RQ1 How does electrostatic crosstalk from neighboring gates influence the Larmor frequency of spin qubits in CMOS quantum dot arrays?
• RQ2 What is the role of spin-orbit coupling in transferring electric field effects to the spin g-factor in silicon-based qubits?
• RQ3 How does the direction of the magnetic field affect the coupling of electric noise to spin qubits and the resulting $ T_2^* $ dephasing times?
• RQ4 What is the impact of local interface disorder on the variability of Stark shift tunability across qubits?
• RQ5 Can a unified framework be established to predict and compensate for gate-induced electric field effects in large-scale spin qubit arrays?

Key findings

• The g-factor of each qubit varies due to local disorder, leading to distinct Stark shift responses depending on gate position and electron displacement direction.
• Electric fields from gates tens of nanometers away induce measurable Stark shifts in qubits via spin-orbit coupling, with tunability dependent on gate and qubit location.
• The [100] crystal orientation of the magnetic field minimizes g-factor variability and reduces electric noise coupling, resulting in higher and more uniform $ T_2^* $ times.
• Measured Stark shift tunability across 30 qubits in nine devices shows excellent agreement with theoretical predictions and $ T_2^* $ profiles, validating the model.
• The framework enables individual qubit control via linear combinations of virtual gates, provided that $ \frac{dg_n}{dV_g} $ is characterized per qubit-gate pair.
• The model breaks down only in cases of valley or orbital degeneracy, where orbital mixing dominates spin-orbit coupling and disorder effects become unpredictable.